The isolation and sequence determination of a new 2S albumin storage protein from Ricinus communis seeds is described. The fragment approach using selective enzymatic cleavage, Edman degradation and mass spectrometry was used to demonstrate primary structure of the 11.3 kDa heterodimer protein which is linked by 4 disulfide bridges. Mass spectrometry (MALDI-TOF and ESI/MS) were used to obtain the molecular weight of the protein and its two constituent chains as a criterion for validating the sequence of each chain obtained by wet chemistry. The sequence of the amino terminal blocked peptide <Gln Gln Gln Glu was determined by ESI/MS which was impossible to do by wet chemistry. The characterization of the second 2S albumin, from R communis seeds demonstrates that the 237 residue precursor protein postulated on the basis on cDNA data codes for two different heterodimer proteins containing approximately 97 residues. A manuscript describing this work has been published J.G odinho da Silva, Jr., O.L.T. Machado, C. Izumi, J.C. Padovan, B.T. Chait, U.A. Mirza & L.J. Greene "Amino acid sequence of a new allergenic 2S albumin storage protein from Ricinus communis which is part of a 30 kDa precursor protein" Archives of Biochem. & Biophys. 336 (1996) 10-18.